1. Field of Invention
This invention pertains to sewage treatment systems, and particularly to means for recirculating liquids and/or activated sludge in such systems as well as the collection and removal of excess sludge from such systems.
2. Prior Art and Other Considerations
U.S. Pat. No. 4,211,657 to Etlin describes a sewage treatment system wherein the recirculation of waste water and/or sludge among various chambers of the system is occasioned by a pressure differential created between the chambers. The extent of the pressure differential depends on various factors, including the water level differential between the chambers; the distance between the chambers; and the velocities of the liquid; and, the diameters of the passageways between chambers.
Other patents disclosing sewage treatment systems include U.S. Pat. Nos. 3,204,768 to Daniel; 3,682,313 to Abraham et al.; 3,709,363 to Smart et al.; 2,987,186 to Burgoon et al.; 4,436,632; 4,362,625; and 4,383,922 to Beard; 3,385,444 to Bufournet; and, 3,043,433 to Singer. Many of these patents disclose recirculation of liquid between chambers through conduits, with discharge ends of the conduits being submerged in liquid. Submersion of a discharge end of such a conduit requires displacement of liquid from around the discharge end. Accordingly, the velocity of recirculation of the liquid through the system is retarded, thereby reducing the efficiency of the system.
Others of these patents require expensive and cumbersome apparatus in order to induce a recirculation effect. Typically the required structures, such as an eductor or a special pump or the like, must be specially constructed and operated at high velocities in order to achieve recirculation. These constructural and operational constraints are uneconomical and can lead to operational problems.
Accordingly, it is an object of the present invention to provide a sewage treatment system and method of operation thereof which facilitates efficient recirculation of liquid through the chambers of the system.
An advantage of the present invention is the provision of a sewage treatment system and method of operation thereof which does not require the use of special liquid pumps or eductors.
A further advantage of the present invention is the provision of a sewage treatment system and method of operation thereof which is not as dependent upon the liquid level between chambers comprising the system, or of the distance between such chambers.
Yet another advantage of the present invention is the provision of a sewage treatment system and method of operation thereof from which excess sludge can be removed economically.
Yet another advantage of the present invention is the provision of a sewage treatment system which is easily constructed.